This invention relates to a fuel injection valve arrangement to be connected with a common rail of a fuel feeding system of a reciprocating internal combustion engine.
So called needle valves, in which the valve member is elongated and quite thin, are commonly used to control fuel injection. Specifically fuel injection arrangements based on a common rail are commonly used and also for example heavy oil may be utilized as fuel. In this kind of known arrangement, injection control is accomplished by a positively controlled needle valve or by a separate control valve positioned before the needle valve and spring loaded needle valve. If a sealing surface of the needle valve in an arrangement based on positive control leaks or the valve needle sticks at its open position, or a sealing surface of a pre-control valve in an arrangement based on a pre-control valve leaks, fuel may leak into the cylinder and serious engine damage may result.
An object of the invention is to provide an injection valve arrangement to be specifically applicable to a fuel injection arrangement based on a common rail, which is reliable, with which the injection procedure is better controllable and by means of which drawbacks of known arrangements may be substantially eliminated.
According to the invention, the injection valve arrangement comprises a first valve needle and a first piston arrangement connected thereto, and a second valve needle and a second piston arrangement connected thereto. The needle valves are arranged operationally in series so that the first needle valve is connected to feed pressure of the common rail and is arranged to open always first. The second needle valve controls the injection of fuel into a cylinder of the engine. The solution based on two needle valves in series, in which the injection takes place only when both of the valves are simultaneously open, is considerably safer than a construction with one valve, because the possibility of leakage or of both valves sticking at the open position simultaneously is substantially less. The two needle valves operate under different conditions. During opening of the first needle valve, the pressure difference over the first valve needle is very small, because the second needle valve is still closed. During opening of the second needle valve, the conditions correspond to those during opening of the conventional injection valve with one needle in a common rail system.
Preferably, the valve arrangement is controlled so that after the injection the first needle valve also closes last. Thus the second needle valve always controls the injection and there is no flow over the sealing surface of the first needle valve during its closing stage, because the second needle valve has already been closed. In this manner, simultaneous malfunction of the two needle valves due to different operation conditions is rendered even more improbable, which results in accurate control of the injection process and increased safety.
In practice each piston arrangement preferably comprises a main piston device to be connected with a valve needle, and an auxiliary piston connected to the main piston device so that a pressure chamber, which has been connected with control pressure through a constriction channel, is formed therebetween. The auxiliary piston is preferably spring loaded in direction away from the main piston device.
A preferred expedient for causing the first needle valve to open first, is for the main piston device of the first needle valve to be of smaller diameter than the main piston device of the second needle valve.
The constriction channel may advantageously be formed in the auxiliary piston. The auxiliary piston may be influenced by another pressure chamber, into which the constriction channel opens.
The other pressure chamber is connected to control pressure through a constriction channel and it is additionally connectable to control pressure over a separate constriction channel, which the auxiliary piston opens for closing the needle valve. Since the diameter of the constriction channel in connection with piston arrangement of the first needle valve, opened by the auxiliary piston, is preferably smaller than the diameter of the corresponding constriction channel in connection with the piston arrangement of the second needle valve, the first needle valve closes after the second needle valve. Because in this manner the opening and closing of the needle valves are accomplished by substantially different means, they can be effected independently of each other.
The control of the piston arrangements may advantageously be accomplished by means of a hydraulic oil arrangement or the like, which acts on both of the piston arrangements, and by means of a separate control valve, by means of which the pressure chambers influencing the piston arrangements are connectable selectively to substantially lower pressure, preferably to atmospheric pressure. In practice the hydraulic oil arrangement may be for example a part of lubrication system of the engine. Because the pressure of the lubrication oil circuit is typically about 7 bar, a booster pump, by means of which the pressure may be increased to a level of about 200 bar, is thus required.
The pressure chambers influencing the first piston arrangement and the pressure chambers influencing the second piston arrangement are separated from each other and connected to the control valve by separate constriction channels. Since there are two separate constriction channels in the arrangement according to the invention, only one control valve, which is preferably a solenoid valve, is needed.